1. Field of the Invention
This invention relates to processes for preparing disalts of dimercaptoisothiazoles, processes for preparing dimers and diisothiazoles from the disalts, and novel isothiazole dimers.
2. Prior Art
1. U.S. Pat. No. 3,197,472 issued July 27, 1965 to R. D. Vest describes a salt of 3,4-dimercaptoisothiazole-5-carbonitrile as the co-product of the reaction of p-dithiino [c]-isothiazole-3,5,6-tricarbonitrile with potassium dimethyldithiocarbamate. This co-product was not further identified or characterized. ##STR1##
2. Coassigned application Ser. No. 719,833, filed Sept. 7, 1976, which is a continuation-in-part of Ser. No. 625,132, filed Oct. 23, 1975, now abandoned discloses alternative processes for preparing 1,4-dithiino[2,3-c; 6,5-c']diisothiazole-3,7-dicarbonitrile, and claims this compound, the corresponding dicarboxylic acid and the parent heterocycle as compositions of matter.
3. U.S. Pat. Nos. 3,149,107 (Sept. 15, 1964), 3,230,229 (Jan. 18, 1966) and 3,232,935 (Feb. 1, 1966) all issued to W. R. Hatchard, and W. R. Hatchard, J. Org. Chem., 28, 2163 (1963), 29, 660, 665 (1964) disclose that the reaction of dimercaptomethylenemalonitrile disodium salt (a structural isomer of Bahr's salt) with sulfur in hot methanol gives 3,5-dimercaptoisothiazole-4-carbonitrile disodium salt (a structural isomer of 3,4-dimercaptoisothiazole-5-carbonitrile disodium salt). ##STR2##
Because of its structure, the described isomer cannot dimerize in the same way as the compound described herein, and consequently it is not convertible to 1,4-dithiino[2,3-c; 6,5-c']diisothiazole-3,7-dicarbonitrile. 3,5-Dimercaptoisothiazole-4-carbo nitrile and its derivatives are also described by E. Soderback, Acta Chem. Scand., 17, 362 (1963), G. A. Hoyer and M. Kless, Tetrahedron Letters, 4265 (1969) and British Pat. No. 1,124,545 (Aug. 21, 1968 to E. Merck).